1. Field of the Invention
The present invention relates to a sintered aluminum nitride material and a substrate of microcircuits or integrated circuits which is manufactured by using the sintered aluminum nitride material, particularly to a sintered aluminum nitride material with strength, high density and good heat transfer characteristics which can be manufactured by using low temperature sintering, and a circuit substrate manufactured by using the sintered aluminum nitride material.
2. Description of the Prior Art
Conventionally, circuit substrates with alumina (Al.sub.2 O.sub.3) as the base material has been used in electronic equipment witch the object of mounting electronic devices such as ICs, LSIs, and the like, fabricating circuits, and insulation. However, since the alumina base material has a low thermal conductivity of about 20 W/m.multidot.K which is insufficient for the highly integrated circuit like LSI to radiate heat from the electronic device.
In the above circumstances, a great deal of attention is now being paid to the realization of circuit substrates utilizing a base material formed from an aluminum nitride (AlN) sintered product with a high thermal conductivity which can cope with the densification and high integration of LSIs which has been taking place in recent years.
However, aluminum nitride exhibits strong covalent bonding and is a difficult material to sinter. Therefore, the minimum sintering temperature of 1800.degree. C. is indispensable in obtainig a finely sintered body.
In order to improve this situation, Japanese Laid-Open Patent Application No. 61-117160 discloses a method whereby low temperature sintering is provided using a raw material in which an oxide of rare earth elements and an oxide of alkaline earth elements are added to an aluminum nitride powder. The sintering temperature of this method is 1,700.degree. C. or less. However, this creates a problem inasmuch as there is a tendency toward staining and the like within the sintered body, and thermal conductivity of the sintered material obtained by the above method is quite low. In addition, when the circuit substrate is adopted for a semiconductor element package, there is even the problem that the sealing characteristics deteriorate in the process of glass-sealing a cap onto the base material, the aluminum nitride sintered body, of the circuit substrate.
In addition, Japanese Laid-Open Patent Application No. 62-153173 discloses the provision of high densification and high thermal conductivity in the aluminum nitride sintered body obtained by using a raw material to which at least one type of material selected from elements in group IVa, group Va, group VIa, group VIIa, and group VIII of the periodic table is added to an aluminum nitride powder. However, strength of the sintered body obtained above is insufficient and the surface of the sintered body is rough. In addition, this is also dissatisfactory in glass-sealing characteristics for use as a material of circuit substrate in fabrication of packages.
Moreover, Japanese Laid-Open Patent Application No. 2-275765 discloses a raw material in which an oxide of elements in group IIIa and an element selected from lithium, beryllium, magnesium, boron, silicon, sulfur, phosphorus, arsenic and zinc are added to an aluminum nitride powder. However, the sintered material has a poor strength. Moreover, densification and heat conduction of the sintered material are still insufficient.
Japanese Laid-Open Patent Application No. 4-130064 discloses addition of manganese to the raw aluminum nitride material in order to improve the coloration of the sintered aluminum nitride with large heat conduction. However, there is no prospect of improvement in the strength and the glass sealing characteristics.